Glow plug

ABSTRACT

An improved glow plug construction and product, comprising the combination of a cylindrical housing body having a central axial bore extending therethrough, with a section of said bore of reduced diameter forming an internal shoulder adjacent the terminal end; a hollow sleeve positioned in close fitting telescoping relationship within said housing bore abutting against the shoulder and extending therein a substantial length of the larger diameter bore section; and, a heater sheath containing an electrical heating element and having an end inserted within the housing bore in close fitting telescoping relationship therewith and abutting against the end of the sleeve. The heater sheath is affixed to the adjacent end of the housing by suitable bonds. An electrical conductor is connected to the heating element and extends concentrically back through the length of the sleeve and central bore of the housing, and is supported by an insulative bushing, to an outer connecting terminal, and the annular space within the hollow sleeve in the central bore around the conductor is packed with an appropriate electrically insulative material, such as magnesium oxide.

Unite States Patent [1 1 Baxter July 31, 1973 i 1 crow PLUG Robert David Baxter, Shelbyville, Ind.

221 Filed: May 15,1972

2] Appl,No.:253,535

[75] Inventor:

[52] US. Cl. 317/98, 123/145 A [51] Int. Cl. F23g 7/00, F23g 7/06, F23g 7/22 [58] 'Field of Search 317/98; 123/145, 123/145 A; 431/263 [56] References Cited UNITED STATES PATENTS 2,884,920 5/1959 Moule et al 123/145 A 3,158,787 11/1964 Testerini 317/98 3,164,748 1/1965 Testerini 317/98 1,632,314 6/1924 Rudqvist 123/145 A 2,140,943 12/1938 Rudqvist 123/145 A 2,492,755 12/1949 McCollum 317/98 2,506,768 5/1950 Bentz et a1 123/145 'A X 3,017,541 1/1962 Lawser 317/98 3,296,496 1/1967 Baxter et a1. 317/98 FOREIGN PATENTS OR APPLICATIONS 611,559 10/1960 ltaly 317/98 1,119,598 12/1961 Germany 317/98 1,242,578 8/1960 France 123/145 A Primary ExaminerVolodymyr Y. Mayewsky Att0meyRaymond G. Simkins et al.

[57] ABSTRACT An improved glow plug construction and product,

comprising the combination of a cylindrical housing body having a central axial bore extending therethrough, with a section of said bore of reduced diameter forming an internal shoulder adjacent the terminal end; a hollow sleeve positioned in close fitting telescoping relationship within said housing bore abutting against the shoulder and extending therein a substantial length of the larger diameter bore sectiomand, a heater sheath containing an electrical heating element and having an end inserted within the housing bore in close fitting telescoping relationship therewith and abutting against the end of the sleeve. The heater sheath is affixed to the adjacent end of the housing by suitable bonds. An electrical conductor is connected to the heating element and extends concentrically back through the length of the sleeve and central bore of the housing, and is supported by an insulative bushing, to an outer connecting terminal, and the annular space within the hollow sleeve in the central bore around the conductor ispacked with an appropriate electrically insulative material, suchas magnesium oxide.

8 Claims, 2 Drawing Figures GLOW PLUG BACKGROUND or? THE INVENTION This invention isdirected to an improved glow plug construction and product for use in starting up compression ignition internal combustion engines, such as those commonly referred to as diesel engines which utilize fuels of a relatively low degree of volatility, and in other heating or igniting applications. The invention provides a more effective and enduring product which is also of lower cost in both materials and assembly resulting from its novel design.

The extreme environmental conditions encountered by glow for in normal internal combustion engine service, comprising their exposure to very high temperatures and pressures as well as the corrosive action of hot combustion "gases, requires that the electrical resistance heating element thereof be protected by being ensheathed within an enclosure, and the enclosing sheath itself must in turn effectively endure such aggressive conditions of exposure over long periods of use. This heretofore required the application of expensive special metal alloys such as Haynes Alloy (Haynes Stellite Companys cobalt-based alloys) for the exposed heater protecting sheath, as well as the use of the alloys in relatively heavy wall thicknesses, all of which increases cost. Also, to endure the engine vibrations and physical shock for adequate service life, it has been necessary to design the units so that the components of the plug reinforce each other to attain strength and rigidity, and to secure the unions therebetween. Commonly this self-reinforcement for strength and rigidity, and security of component unions has been heretofore attained by extending the heater sheath, normally of necessity constructed from very costly alloys, a sub stantial distance back into the body of the outer housing to provide an extensive area of intermediate overlapping therebetween. This further increases the amount of costly alloys needed for the sheath.

Moreover, because of the extreme engine vibrations encountered in this service, many prior constructions required the filling of internal voids, generally comprising the area between the central electrical conductor and surrounding structure walls, with an insulating cement such as Sauereisen cement. Otherwise the vibrations tend to cause the central conductor or terminal to loosen in time, and work its way up and out of the unit. Such cements generally must be introduced into the unit by means of a hyperdermic needle or syringe type of device to carry the cement material to all regions throughout the assembly. To ensure complete filling and avoidance of air bubbles or voids, it has also been necessary to either centifuge or vibrate the assembly.

subsequent to introduction of such a cement material.

SUMMARY OF THE INVENTION This invention comprises a novel glow plug product design and construction of a specific combination and arrangement of components. It includes a glow plug housing having its central axial bore provided with an integral internal shoulder adjacent to its outer or connective terminal end, and a close fitting hollow sleeve of a relatively low cost material telescoped within said bore and extending a substantial length of the housing preferably from abutment against the said internal shoulder to a region relatively near the housings opposite end. The sleeve in turn provides an abutment for sheath inserted into the bore with the result that the protective sheath unit penetrates the housing bore only a limited predetermined distance. This arrangement achieves maximum effectiveness of the combined components at a minimum material cost, as well as providing the interdependent component reinforcement for overall strength and rigidity of the unit and security of the unions joining its respective components. Additionally this relatively uncomplicated construction, including the long sleeve section, can be easily and effectively filled throughout the entire internal cavity length with magnesium oxide, or other apt particulate electrically insulative material such as beryllium oxide, boron nitride, or aluminum oxide, to effectively support and rigidly fix the central electrical conductor so that it resists vibratory motion and physical shock without need for cement and the complications of its application.

OBJECTS OF THE INVENTION Accordingly it is the primary object of this invention to provide an effective glow plug product which is more stable in its construction and longer lasting in service, and more economical in lower material costs attributed to the reduced amount of expensive alloys which need be utilized and due to simplified manufacturing assembly measures.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other obvious advantages of this invention will be apparent from the following description and accompanying drawings in which:

FIG. 1 is a general side elevational view of a glow plug constructed according to this invention; and

FIG. 2 is a partial axial sectional view of the glow plug of FIG. 1 showing detailes of the construction de sign and arrangement of components.

DESCRIPTION OF A PREFERRED EMBODIMENT A glow plug construction according to this invention is illustrated in the drawing as 10, comprising a housing 12 having an externally threaded section 14 to secure the plug into an engine cylinder block or other structure in operating position, such as within the inlet port of a precombustion chamber of a compression ignition engine. As seen in FIG. 2, the housing 12 is provided with a central axial bore 16 extending through the length thereof; Axial bore 16 is formed in two sections of different internal diameters, section 18 adjacent the heater end of the housing being of the larger diameter than section 20 adjacent to a connective terminal 24, with the interface between the sections of different internal diameter forming a step portion providing an annular integral shoulder 22 about the interior of the bore 16.

A hollow cylindrical sleeve 26 is concentrically contained within the larger bore section 18 of the axial bore 16 of the housing in close fitting telescoping arrangement therewith, and is positioned therein generally intermediate the length of axial bore 16 with an innermost end preferably in abutting contact with shoulder 22, and an outer end spaced inwardly from the end of the housing 12. The shoulder 22 provides a stop limiting the sleeves axial movement through the bore 16 in a direction towards the outer connective terminal posed of stainless steel or similar high temperature resistance, but relatively low cost metal or alloy.

The open end of a generally elongated protective metal sheath 28, for the confinement of an electrical heater element 30, is inserted in close fitting telescoping arrangement in the larger diameter section 18 of the housing bore 16 with its end portion extending therein a predetermined distance and in abutting contact with the adjacent end of the sleeve 26. The protective sheath 28, which is normally exposed directly to the extreme environmental conditions of a combustion engine and encounters the very high temperatures and pressures as well as the corrosive action from the combustion gases, must be composed of a very durable and resistant metal to attain long and effective service life. Typical apt metals for such severe service comprise Haynes or like alloys which are relatively costly. Ac-

cordingly the depth or distance of the end portion of sheath 28 extending into the housing 12 can be limited or governed by the length of sleeve 26, thereby enabling reduction of the amount of the higher cost material required for the protective sheath. By securely affixing the annular end of housing 12 to the outer surface of sheath 28 as by brazing and joining at 34, and preferably also affixing the abutting ends of sleeve 26 and sheath 28 together, such as joining them by welding or other bonding techniques, illustrated as weld 32 in the drawing, the distance that sheath 28 needs to project'inwardly into bore 16 can be significantly reduced without impairing the strength or rigidity of the overall plug structure and the reinforcing relationship of its components.

An electrical heating element 30, typically comprising a coiled helical electrical resistance wire, is located within the protective sheath 28 with one electrical contact terminal of the heater element conductively connected to the inside tip of the sheath. The other electrical contact terminalof the element 30 is conductively connected to electrical conductor 36 which extends centrally back through hollow sleeve 26 and the axial bore 16 of housing 12, in spaced apart relationship therewith and is electrically connected to the outer connective terminal 24. Conductor 36 passes centrally through an electrical insulating bushing 38 positioned within an end counterbore or rt avity 40 adjacent the termination of bore 16. An annularw'asher 42, spaced apart from central conductor 36 passing therethrough, is positioned within counterbore 40 and the annular end of housing 12 is turned inwardly to form a retaining flange 44. An electrically insulative washer 46 separates the housing 12 from the outer connective terminal 24.

The length of sleeve 26 corresponds substantially to the length of central conductor 36 which extends through the axial bore 16, and conductor 36 is therefore effectively supported and rigidly held in its axial position, so as to resist vibration and physical shock as well as being electrically isolated, by filling and compacting the annular space about the conductor within the sleeve and/or housing bore with a granular electrically insulative material 48 such as magnesium oxide, beryllium oxide, boron nitride, aluminum oxide, or the like. i

This construction obviates the need for the more involved application of a cement and accompanying necessary precautionary measures, provides a substantial savings in both material and assembly costs, which together with the additional savings of reducing the quantity of expensive material required for the protective sheathing, produces a glow plug of undiminished performance and durability at a significant economy.

A further advantageous feature of the glow plug construction of this invention is that the inside diameter of the housing bore is smaller at the connective terminal end than at the heater end, and should the bond at affixes which affixed the heater sheath to the outer housing fail, the sheath is blocked by the internal shoulder and following smaller diameter of the bore from vibrating or otherwise being caused to move through the housing toward the connection terminal 24. Also, it will be apparent from the foregoing that the present invention provides for positively affixing and holding the sheath and heater element firmly in position and in an arrangement wherein the elements complement each other to produce in concert a structure of improved strength and integrity. Moreover this construction provides ample electrical clearance between the central conductor 36 and the sleeve 26, including the location where the central conductor emerges from the sleeve, permitting the use of a thinner wall tube for the sleeve 26.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A glow plug comprising:

a. a generally cylindrical metal housing having an axial bore extending therethrough and provided with an internal shoulder;

b. an elongated heater protecting metal sheath having a closed outer end and with a portion of the opposite open end extending into said axial bore of the housing and engaging it in close fitting telescopic arrangement, said housing being affixed to the sheath;

. a hollow cylindrical metal sleeve concentrically contained within said axial bore of the housing and extending therein a substantial length with an end abutting the said end portion of said heater sheath extending into the bore whereby the length of the said sleeve predetermines the distance the said sheath extends into the axial bore;

d. an electrical heating element positioned within said heater sheath having one terminal end electrically connected to the outermost end of said heater protecting sheath and the other terminal end in electrical contact with a conductor extending from said element through the axial bore of the housing spaced apart from the housing and sleeve contained therein and in contact with a terminal;

an electrical insulating material substantially filling the space within the sleeve and the sheath; and,

f. an insulative bushing member positioned within I the central axial bore of the glow plug housing adjacent to its end opposite the heating element, and said conductor extending through the insula tive bushing and being electrically connected with said terminal.

2. The glow plug as defined in claim 1 wherein the electrical insulative material comprises magnesium oxide.

3. The glow plug as defined in claim 2 wherein the electrical heating element positioned within said heater protecting sheath is a helical electrical resistance element.

4. The glow plug as defined in claim 3 wherein the end of the generally cylindrical housing receiving a portion of the heater protecting sheath within its axial bore is affixed to the said heater sheath received therein and the abutting ends of the said heater sheath and hollow cylindrical sleeve are affixed to each other.

5. The glow plug as defined in 'claim 4 wherein the internal shoulder provided within the central axial bore of the housing comprises an annular abutment formed by a section in said axial bore of reduced diameter.

6. A glow plug for use with compression ignition engines comprising:

a. a generally cylindrical metal housing adapted to be secured to the body of said engine, said housing having an axial bore extending therethrough and provided with an internal shoulder;

b. an elongated heater protecting metal sheath having a closed outer end and with a portion of the opposite open end extending into said axial bore of the housing and engaging it in close fitting telescoping arrangement, said housing being affixed to the sheath;

c. a hollow cylindrical metal sleeve concentrically contained within said axial bore of the housing and positioned intermediate thereof with its ends abutting with each the internal shoulder of the bore and the said end portion of the heater sheath extending into the bore whereby the length of the sleeve predetermines the distance the said sheath extends into the axial bore, said sleeve end abutting the end portion of the sheath being affixed thereto;

d. an electrical heating element positioned within said heater sheath having one terminal end electrically connected to the outermost end of the said heater protecting sheath and the other terminal end electrically connected to a conductor extending from said heating element centrally through the axial bore of the housing and spaced apart from the housing and sleeve contained therein and making electrical contact with a terminal connector;

e. an electrical heating element positioned within said heater sheath having one terminal end electrically connected to the outermost end of said heater protecting sheath and the other terminal end in electrical contact with a conductor extending from said element through the axial bore of the housing spaced apart from the housing and sleeve contained therein and being in electrical contact with a terminal; and

f. an electrical insulating material substantially filling the space within the sleeve and the sheath.

7. A glow plug comprising:

a. a generally cylindrical metal housing having an axial bore extending therethrough and provided with an internal shoulder;

b. an elongated heater protecting metal sheath having a closed outer end and with a portion of the opposite open end extending into the axial bore of the housing and engaging it in close fitting telescoping arrangement, said housing being affixed to the sheath;

c. a hollow cylindrical metal sleeve concentrically contained within said axial bore of the housing in close fitting telescoping arrangement therewith, positioned inermediae and extending a substantial length in said bore with one end abutting the internal shoulder of the bore and the other end abutting the open end of the portion of the heater protective sheath extending into said bore;

d. an electrical heating element positioned in said heater sheath having one terminal end electrically connected to the closed outermost end of the sheath and the other terminal end in electrical contact with a conductor extending from said element through the axial bore of the housing spaced apart from said housing and sleeve contained therein and connecting with a terminal connector;

e. electrical insulating material substantially filling the space within the sleeve and the sheath; and

with the sleeve and the sheath; and

an insulating bushing member positioned within the axial bore of the glow plug housing adjacent to the end opposite that receiving a portion of the heater protecting sheath, and said conductor extending through the insulating bushing and being electrically connected with the terminal connector.

8. The glow plug as defined in claim 7 wherein the end portion of the said heater protecting sheath extends only a short predetermined distance into the axial bore of the housing relative to the length of the extending portion thereof.

I EBT RATE Inventor(s I I 7 Robeft D. Baxter I It is certified thet er for appea re in the above-identifiedpatentr and that said-Letters Patent are hereby corrected as shown below:

C0lumn 6, line vl8, "inermediee" should be ifi flermedi'ate I A line. 33,? I "with the sleeve and the sheath; and" shbuld be deleted Signed 1 973.

(SEAL) e Attest:

EDWARD M.FLET(CHERI,J\R. v t I RENEgD. TEGTMEYER Attes tinghOffi cer I -Acting- Commissioner f-Paten Ms-)0 mite-Enemies i-ATBNT ow es QERTEFICATE 0F meme-T Patent No. 3,749,98 Dat d Julv InVen Robeft D. Baxter It is certified that error appears in the above-identiifiedpatentand that said Letters Patent are hereby corrected as shown" below:

Column 6, line 18, "inermediae" should be ig'ij tgermediate line 33, "with the sleeve and the sheath; and" should be deleted Signed and sealed this 18th day of Deeember 1973.

(SEAL) Attest: v

EDWARD M. FLETCHERJR. RENE D. TE GTMEYER Attesting Officer Acting Commissioner of Pat 

1. A glow plug comprising: a. a generally cylindrical metal housing having an axial bore extending therethrough and provided with an internal shoulder; b. an elongated heater protecting metal sheath having a closed outer end and with a portion of the opposite open end extending into said axial bore of the housing and engaging it in close fitting telescopic arrangement, said housing being affixed to the sheath; c. a hollow cylindrical metal sleeve concentrically contained within said axial bore of the housing and extending therein a substantial length with an end abutting the said end portion of said heater sheath extending into the bore whereby the length of the said sleeve predetermines the distance the said sheath extends into the axial bore; d. an electrical heating element positioned within said heater sheath having one terminal end electrically connected to the outermost end of said heater protecting sheath and the other terminal end in electrical contact with a conductor extending from said element through the axial bore of the housing spaced apart from the housing and sleeve contained therein and in contact with a terminal; e. an electrical insulating material substantially filling the space defined by the axial bore of the housing with the sleeve and the sheath, and an insulative bushing member positioned within the central axial bore of the glow plug housing adjacent its end opposite the heating element and said conductor passes through the insulative bushing and makes electrical contact with said terminal.
 2. The glow plug as defined in claim 1 wherein the electrical insulative material comprises magnesium oxide.
 3. The glow plug as defined in claim 2 wherein the electrical heating element positioned within said heater protecting sheath is a helical electrical resistance element.
 4. The glow plug as defined in claim 3 wherein the end of the generally cylindrical housing receiving a portion of the heater protecting sheath within its axial bore is affixed to the said heater sheath received therein and the abutting ends of the said heater sheath and hollow cylindrical sleeve are affixed to each other.
 5. The glow plug as defined in claim 4 wherein the internal shoulder provided within the central axial bore of the housing comprises an annular abutment formed by a section in said axial bore of reduced diameter.
 6. A glow plug for use with compression ignition engines comprising: a. a generally cylindrical metal housing adapted to be secured to the body of said engine, said housing having an axial bore extending therethrough and provided with an internal shoulder; b. an elongated heater protecting metal sheath having a closed outer end and with a portion of the opposite open end extending into said axial bore of the housing and engaging it in close fitting telescoping arrangement, said housing being affixed to the sheath; c. a hollow cylindrical metal sleeve concentrically contained within said axial bore of the housing and positioned intermediate thereof with its ends abutting with each the internal shoulder of the bore and the said end portion of the heater sheath extending into the bore whereby the length of the sleeve predetermines the distance the said sheath extends into the axial bore, said sleeve end abutting the end portion of the sheath being affixed thereto; d. an electrical heating element positioned within said heater sheath having one terminal end electrically connected to the outermost end of the said heater protecting sheath and the other terminal end electrically connected to a conductor extending from said heating element centrally through the axial bore of the housing and spaced apart from the housing and sleeve contained therein and making electrical contact with a terminal connector; e. an electrical heating element positioned within said heater sheath having one terminal end electrically connected to the outermost end of said heater protecting sheath and the other terminal end in electrical contact with a conductor extending from said element through the axial bore of the housing spaced apart from the housing and sleeve contained therein and being in electrical contact with a terminal; and f. an electrical insulating material substantially filling the space defined by the axial bore of the housing with the sleeve and the sheath.
 7. A glow plug comprising: a. a generally cylindrical metal housing having an axial bore extending therethrough and provided with an internal shoulder; b. an elongated heater protecting metal sheath having a closed outer end and with a portion of the opposite open end extending into the axial bore of the housing and engaging it in close fitting telescoping arrangement, said housing being affixed to the sheath; c. a hollow cylindrical metal sleeve concentrically contained within said axial bore of the housing in close fitting telescoping arrangement therewith, positioned inermediae and extending a substantial length in said bore with one end abutting the internal shoulder of the bore and the other end abutting the open end of the portion of the heater protective sheath extending into said bore; d. an electrical heating element positioned in said heater sheath having one terminal end electrically connected to the closed outermost end of the sheath and the other terminal end in electrical contact with a conductor extending from said element through the axial bore of the housing spaced apart from said housing and sleeve contained therein and connecting with a terminal connector; e. electrical insulating material substantially filling the space within the sleeve and the sheath; and f. an insulating bushing member positioned within the axial bore of the glow plug housing adjacent to the end opposite that receiving a portion of the heater protecting sheath, and said conductor extending through the insulating bushing and being electrically connected with the terminal connector.
 8. The glow plug as defined in claim 7 wherein the end portion of the said heater protecting sheath extends only a short predetermined distance into the axial bore of the housing relative to the length of the extending portion thereof. 